1. Technical Field
The present invention relates to a ball bearing assembly for a bicycle, and more particularly, to a ball bearing assembly characterized by improved assembling accuracy and automatic center adjusting function.
2. Description of Related Art
The exposition of ball bearing assembly is herein started with a bicycle headset structure, as shown in FIGS. 1 and 2, implementing an upper ball bearing assembly 20 and a lower ball bearing assembly 10.
As can be seen in the drawings, the lower ball bearing assembly 10 comprises an outer race 11, a ball cage 12 and an inner race 13. The inner race 13 is mounted onto a socket 92 positioned between a front fork stem 90 and a front fork 91 of the bicycle. Sequentially, the ball cage 12 is mounted onto the inner race 13 and the outer race 11 is combined with the bottom edge of a head tube 93 of the bicycle. As the front fork stem 90 is pierced into the head tube 93, the ball cage 12 can be firmly positioned between the outer and inner races 11, 13. Regarding the upper ball bearing assembly 20, it includes an outer race 21, a ball cage 22, an inner race 23, a cap 24 and a packing ring 25. The outer race 21 is for being engaged to the top of the head tube 93, and sequentially, the ball cage 22 is settled upon the outer race 21. Said cap 24 presses the top edge of the inner race 23 by a shallow annular grove 241 formed thereon, and the inner race 23 downward pressed on the ball cage 22, whereupon when the packing ring 25 is inserted form a center hole 242 of the cap 24 to compress the inner periphery of the inner race 23, the inner race 23 can be secured with the cap 24 while presses firmly on the ball cage 22. Lastly, the front fork stem 90 is pierced into the packing ring 25 so as to be combined with a head stem (not shown).
According to the previously discussed headset structure, the assembly of the upper ball bearing assembly 20 is dependent on the structure that the cap 24 simply contacts the top edge of the inner race 23 by the annular grove 241. That is to say, there is no any direct and reliable positioning mechanism between the inner race 23 and the cap 24 and the combination therebetween can only be committed to the packing ring 25.
However, some material or structural properties of conventional packing ring 25 might incur problems. For instance, an aluminum-made packing ring 25 can easily suffer deformation due to external force or temperature variation. Also can be noted is a gap 251 provided thereon for flexibly balancing compression force generated by the center hole 242 and the inner periphery of the inner race 23. Nevertheless, the relevant stress can be converged to the point on the packing ring 25 where is opposite to the gap 251, and this may play some role in the deformation of the packing ring 25. Thus it can be seen that the conventional packing ring are subject to deformation and poor structural stability. With such a conventional packing ring, the fastening between the inner race and ball cage can be consequently affected and therefore the assembling accuracy of the entire ball bearing assembly can be in turn depressed.